Laterite nickel and cobalt ore deposits generally contain oxidic type ores, limonites, and silicate type ores, saprolites, as two layers in the same deposits, separated by a transition zone. To minimise the equipment size for processing either the saprolites or the limonites by commercial processes, high grade limonite and saprolite are preferred. This leads to many ore bodies and transition ores in some deposits being rejected for current process routes.
The higher nickel content saprolites tend to be treated by a pyrometallurgical process involving roasting and electrical smelting techniques to produce ferro-nickel. The power requirements and high iron to nickel ore ratio for the lower nickel content limonite, saprolite, and limonite/saprolite blends in the transition zone make this processing route too expensive.
The high nickel and cobalt content limonite is normally commercially treated hydrometallurgically by the High Pressure Acid Leach (HPAL) process, or by a combination of pyrometallurgical and hydrometallurgical processes, such as the Caron reduction roast—ammonium carbonate leach process.
The above processes generally requires “whole ore” processing as there is no effective method to beneficiate the ore. This has the disadvantage that the mineralogical fractions of the ore which may contain lower metal values effectively dilute the total treated ore quality and increase recovery costs.
The conventional treatment of saprolite to produce ferro-nickel, involves a drying step, followed by a reduction roast step to partially convert the nickel oxides to nickel, and smelting in an electrical furnace. This is a highly energy intensive process and requires a high grade saprolite source to make it economic. It also has the disadvantage that financial value of any cobalt in the ore, which is recovered into the ferro-nickel, is not realised. An improvement to this process would be to provide a nickel iron concentrate to the smelting step which would lead to a large reduction in the power consumption, which is one of the major costs of the process.
Heap leaching is a conventional method of economically extracting metals from ores and has been successfully used to recover materials such as copper, gold, uranium and silver. Generally it involves piling raw ore directly from ore deposits into heaps that vary in height. The leaching solution is introduced onto the top of the heap to percolate down through the heap. The effluent liquor is drained from the base of the heap and passes to a processing plant where the metal values are recovered.
Heap leaching of laterites is taught in U.S. Pat. No. 5,571,308 (BHP Minerals International, Inc), which describes a process for heap leaching of high magnesium containing laterite ore such as saprolite.
U.S. Pat. No. 6,312,500 (BHP Minerals International, Inc) also describes a process for heap leaching of laterites to recover nickel, which is particularly effective for ores that have a significant clay component (greater than 10% by weight).
A major problem with the heap leach process is that the leachate produced contains, in addition to the nickel and cobalt values targeted, large quantities of iron and a variety of other impurities. The purification of similar nickel solutions from commercial laterite acid leach processes involve neutralisation of the acid content, precipitation of iron, followed by production of a nickel cobalt intermediate, a re-dissolution step, and complex solvent extraction stages to produce saleable nickel and cobalt. The purification steps generally aim for complete removal of iron and the other impurities.
Ion Exchange (IX) processes have been disclosed for the extraction of both the nickel and cobalt from the nickel leachate, leaving the major impurities in the raffinate.
U.S. Pat. No. 9,516,118 (BHP Minerals International Inc.) describes an ion exchange process for separating nickel from the leachate from treatment of laterite by the pressure acid leach process. Nickel is extracted by the resin at pH less than 2, and stripped with sulfuric acid for subsequent electrowinning. Cobalt remains in the raffinate along with other impurities, and after solution neutralisation is precipitated as a sulfide.
Patent WO 00/053820 (BHP Minerals International Inc.) describes the ion exchange extraction of nickel and cobalt from acid sulfate leach solution onto the resin, and the subsequent acid stripping of the metals from the resin, and their separation by solvent extraction.
U.S. Pat. No. 6,350,420 B1 (BHP Minerals International Inc.) also teaches the use of ion exchange resin in a resin in pulp process to extract nickel and cobalt onto the resin from an acid leach slurry.
The above patents all aim to produce relatively pure nickel solution, or nickel and cobalt strip solutions from the ion exchange resins.
The above discussion of documents, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention before the priority date.
The present invention aims to provide a new process which overcomes or at least alleviates one or more of the difficulties associated with the prior art.